Accelerating master switch



May 22, 1956 F. MEKELBURG 2,747,046

ACCELERATING MASTER SWITCH Filed May 25, 1950 4 Sheets-Sheet l E I EE-IN V EN TOR. Zia/Z .77 A//faZZ 11/:

y 1956 E. F. MEKELBURG 2,747,046

ACCELERATING MASTER SWITCH Filed May 25, 1950 4 Sheets-Sheet 2 INVENTOR.E 4: Z 4 Z'fiZlvfeZZz/c l BY y 2,1956 E. F. MEKELBURG 2,747,046

ACCELERATING MASTER SWITCH Filed May 25, 1950 4 Sheets-Sheet 3 IN V ENTOR. E. 2. 22/2 fuzz/( 62) fly W May 22, 1956 E. F. MEKELBURG 2,747,045

ACCELERATING MASTER SWITCH Filed May 25, 1950 4 Sheets-Sheet 4 MAGNETICCOIL IN V EN TOR.

ACCELERATING MASTER SWITCH Earl F. Mekeiburg, Wauwatosa, Wis., assignorto Square D Company, Detroit, Mich., a corporation of MichiganApplication May 25, 1950, Serial No. 164,281

7 Claims. (Cl. ZOO-98) This invention relates to an accelerating switchfor controlling electric motors, which is particularly useful forcontrolling the operation of electric trucks.

One object of the present invention is the provision of an acceleratingmaster switch in which a plurality of individual switches are operatedby a moving cam, the rate of movement of the cam being determined by atiming mechanism.

Another object of the present invention is the provision of anaccelerating master switch in which a movable cam which operatesindividual switches is rectilinearly movable and which is provided witha timing mechanism which adjustably controls the rate at which the cammay move over varying sections of its travel.

Another object of the present invention is the provision of a switch inaccordance with the preceding objects in which movement of the switchoperating cam is halted by the operation of a polarized relay until thearmature of the electric motor controlled by the accelerating masterswitch reaches a desired rotating condition.

Another object or" the present invention is the provision of anaccelerating master switch employing a coil and a permanent magnet whichact together to inhibit the accelerating operation until such time asthe back E. M. F. in the armature of the associated electric motor hasfallen to a desired level.

Another object of the present invention is the provision of anaccelerating master switch in accordance with the preceding objectswhich employs a plurality of individual snap switches operated by arectilinearly movable cam biased toward the high speed position.

Other objects and features of the invention will be nited States Patentreadily apparent to those skilled in the art from the specification andappended drawings illustrating certain preferred embodiments in which:

Figure 1 is a front elevation of the device of the present inventionwith part of the enclosure in section and part broken away to show theinternal operating members.

Figure 2 is a sectional view along the line IIII of Figure 1.

Figure 3 is a view of the device of the present invention taken from theposition III of Figure 1.

Figure 4 is a sectional view along the line IV-lV of Figure 1.

Figure 5 is a sectional view along the line V-V of Figure 3, and inwhich the cam mechanism has been moved to the opposite extreme from thatshown in Figure 1.

Figure 6 is a sectional view along the line VI-VI of Figure 1.

Figure 7 is a detail sectional view along the line VII- VII of Figure 3,in which the movable cam is the same position as that shown in Figure 5.

Figure 8 is a detail sectional view along the line VIII-VIII of Figure4.

Figure 9 is a detail sectional view along the line IX-IX of Figure 3.

Figure 10 is a diagrammatic representation of a control circuit for anelectric motor employing the device of the present invention.

The device of the present invention comprises an outer enclosing box 1of sectional form and on the back of which there is mounted, as bystuds, a metal base assembly 2. The base assembly 2 is provided with apair of parallel tubular chambers 3 at its opposite sides, in each ofwhich is disposed a strong biasing spring 4, each spring being disposedbetween two spring keepers 10, the upper of which, from the view shownin Figure 2, abuts against the end of the chamber 3, while the lowerspring keeper abuts against a cotter pin 5, which extends through anelongated bar 6, which extends completely through the chamber 3 andprojects from both ends thereof. The bars 6 have a rectangular area cutout therefrom which constitute latching openings 58.

Joining the lower ends of the bars 6 is a coupling 7 which is furtherjoined by screws to a cam shaft 8 having a plurality of camming surfacesthereon as shown in Figure 5. Acted upon by these cam surfaces are aplurality of rollers 9 which are mounted upon laterally extending pins11, the pins joining pairs of arms 12 which project parallel to the camshaft 8 and are located below it, the arms 12 being pivotally mounted tothe base assembly 2 by the pins 13.

Pins 11 serve also to mount generally U-shaped brackets 14 which extendabove the cam shaft 8, with springs 15 being provided within each ofthese U-shaped members 14, the springs 15 acting to bias the bights ofthe members 14 away from the cam shaft 8. The opposite ends of thesprings 15 are mounted upon a supporting member 16, which is mountedupon base assembly 2 above the cam shaft 8.

It will be seen that the springs 15 acting upon the U-shaped members 14serve to maintain the roller members 9 in contact with the cammingsurfaces upon the cam shaft 8. It will further be seen that as the camshaft 8 is rectilinearly moved, the rollers 9 will be moved toward andaway from the center of the cam shaft 8 by the camming surfaces thereonto move these bracket members 14 rectilinearly to the left and to theright as viewed in Figure 5.

Each of the bights of the U-shaped brackets 14 is provided with anoperating button 17 threaded therein and which in the position in whichspring 15 is least stressed, has fully depressed the associatedoperating button 18 of one of snap switches 19, 20 or 21, the snapswitches being mounted upon upstanding projections of the base assembly2. These snap switches are of the double-throw, double-break type, andhave an internal bias acting to press the operating button outward.

The lower end of the cam shaft 8, from the position shown in Figure l,propects through the cover 1 a substantial distance, that portion of thecam shaft which is outside of the cover 1 being protected by a rubberboot which has a flanged edge serving to protect the interior of the box1 from the entrance of undesirable particles. The opposite end of thecam shaft 8 projects above the base assembly 2 and extends into a timingcylinder 22 which is illustrated in Figure 7. The cylinder 22 is fixedlymounted by studs 23 to the upper end of the base assembly 2.

Carried by the upper portion of the shaft 8 is a spring guide 24 aboutwhich is disposed a coil spring 25 which acts against an inner surfaceof a piston 26 which fits tightly within the circular interior sectionof cylinder 22 and is provided with a sealing ring 27 which is disposedabout the periphery of piston 26, the piston 26 being mounted to an endof shaft 8 by means of a screw 3 and sealing washer arrangementgenerally designated at 28.

As will be seen from an inspection of Figure 7, the walls of thecylinder 22 have relatively thick portions which contain thereinelongated passages 29, the outer ends of which are threaded. Each ofthese passages 29 is communicated with the interior of cylinder 22 bymeans of two laterally projecting apertures spaced one from the other.In the specific embodiment illustrated, the cylinder 22 has three suchelongated passages 29 and, hence, six apertures communicating thesepassages with the interior of cylinder 22, with these communicatingapertures being numbered 31 through 36 inclusive. The apertures 31through 36 are spaced so that they, together, extend over the entirelength of the interior of cylinder 22,, with the lower of one pair lyingin the same transverse plane as theupper of the next pair. Thus, it willbe seen from Figure 7 that aperture 32 lies in the same transverse planeas aperture 33, and aperture 34 lies in the same plane as aperture 35.

In each of the passages 29 is an adjusting screw, these being numbered37, 38 and 39. These adjusting, screws terminate in tapered pins whichcooperate with portions of the chambers 29 to limit the free passage ofair from one of the transverse apertures to the other cooperatingaperture through the associated chamber. Each of these adjusting screwsis provided with a knurled head, metallic holding elements 41 beingprovided at one end of the chamber 22 to cooperate with the knurling ofthe adjusting screw head to maintain them in any particular desiredposition, as may be seen in Figure 3.

As will be seen from Figure 2, mounted to upstanding lugs of baseassembly 2 by means of studs 42 is a plugging assembly generallydesignated by means of the numeral 43. This assembly comprises acomposite generally U-shaped bracket 44 of magnetic material in whichthere is mounted a magnet coil 45. The coil 45 surrounds a core ofmagnetic material 48 fixed at one end by a rivet through the compositebracket 44, the opposite end of core 48 being against a magnetic poleface piece 46 mounted between and in the same plane as the ends 47 ofcomposite bracket 44. The pole piece 46 is mounted on ends 47 of bracket44 by a nonmagnetic plate 50.

Coil 45 has terminals 49 and 51, and terminal 49 has connected thereto aflexible conductor 52, the other end of which is adjustably andelectrically connected to an intermediate point on a resistor 53 whichis mounted between the arms of a fiber U-shaped bracket 54. When thedevice is in circuit, terminal 51 is connected to one terminal of thearmature of the electric motor to be controlled, while resistor 53parallels an accelerating resistor connected to the other terminal ofthe armature, as may be seen in Figure 10, and serves as a voltagedivider.

The bracket 44 has rearwardly extending legs at each side thereof whicheach support a pivot pin 55. Each pin 55 pivotally mounts a generallyL-shaped latch 56. hetween one extremity of these latches 56 there ismounted, as by studs 57, an armature assembly which comprises a holdingbracket 59 having upper and lower ledges which mount, as shown in Figure9, two U-shaped pieces of magnetic material 61 and 62 which areseparated -y and mounted to a strong permanent magnet v63. Near theopposite extremity of each of these latches 56 is a notched portion 60which is designed to cooperate with the latching openings 58 of rod 6 ina manner subsequently described.

As an example of the use of the device of the present invention, itsoperation shall be described in a circuit for controlling the tractionmotor of a battery-operated truck. Such a circuit is illustrated inFigure 10. In

this figure, contacts are represented by rectangular boxes,

normally closed contacts being represented by showing two of theserectangular boxes in contact with each other,

while normally open contacts are represented by two of these rectangularboxes spaced apart. All of the contacts marked F are operated by theelectromagnetic coil marked F, the normally open contacts F closing uponenergization of the coil F, while the normally closed contacts F openupon energization of the coil F. Similarly, all of the contacts marked Rare operated by the coil R. In exactly the same manner, the contacts 1Aand 2A are operated by the electromagnetic coils 1A and 2A.

in this Figure 10, the contacts of snap switches 19, 20 and 21 appeardiagrammatically within the dotted box superimposed upon the figure,this dotted box including as well a tabular record of the condition ofeach of the contacts in each of the speed steps accomplished by thedevice of the present invention, with the speed labeled S4 being thehigh speed position. The contacts of switch 19 are labelled 19A and 19B,those of switch 2%) as ZtiA and 203. Only one of the two possiblecontact positions of switch 21 is used, and is labelled 2113 in thediagram.

in the off position of the device, cam shaft 8 has been moved to itsfully retracted position, that shown in Figures 1 and 2, against thebias of the springs 4 by the foot pedal of the electric truck which isbiased by a strong foot pedal spring, the foot pedal being pressedagainst that part of the cam shaft 8 which projects from the lower endof the device. The spring which operates the foot pedal is, of course,stronger than the biasing springs 4 of the device of the presentinvention.

When the electric truck which is controlled by the device of the presentinvention is started from a rest postion, the operator initially closesthe direction switch as, for example, in the forward position. Then asthe operator depresses the foot pedal against the bias of the foot pedalspring, cam shaft 8 will start to move forward under the influence ofthe biasing springs 4, until it reaches the first speed position. inthis position con tacts 21B, which are open in the o position of thedevice, are closed so that an electrical circuit is completed from thesupply battery through contacts ZhA and 19A, through 21B and thedirection selecting switch which is now in the forward position, andthrough the Forward electromagnetic coil indicated by F on the diagramof Figure 10. The energization of coil F causes the normally opencontacts marked F to close, and the normally closed contacts marked toopen in the usual manner. The electric motor is then connected acrossthe source of energy through the conventional accelerating resistors,the coil 45 being energized by the voltage drop across the armature ofthe electric motor. The flux caused by the current flow through the coil45 is in such a direction as to oppose the flux emanating from thepermanent magnet 63. The permanent magnet assembly is therefore repulsedby the coil fiux so as to rotate the latches 56 in a clockwisedirection, from the view of Figure 2, to move the latching toes out ofthe opening 58 of the rods 6,. which then move downwardly under the biasof springs 4 at a rate determined by the timing assembly, the operationof which will be subsequently described.

The back surface of the latching toes of latches 56 then rest upon thetransverse end portions of rods 6, which are then movable free of thelatches.

As the cam shaft 8, coupled to the rods 6, moves, the camming surfacesoperate against the rollers 9 to effect rectilinear movement of thebrackets The operating buttons 17, threaded into the brackets 14, eitherdepress the operating buttons 18 of the snap switches or are retractedfrom the operating buttons of the snap switches to effect the desiredoperation of the contacts of these switches.

As indicated by the table shown in Figure 10, the cam shaft will operatethe switches so that in speed S2 contacts 19A, 20B and 21B are closed.In this speed position, the closure of 203 energizes the electromagneticcoil 1A, energization of this coil 1A effecting closure of the normallyopen contacts ltbelled 1A, and opening the normally closed contactslabelled 1A thereby cutting out some of the resistance in series withthe armature of the electric motor.

Cam shaft 8 continues to move forward at a timed rate, under theinfluence of the biasing springs 4 to the speed S3 position, operatingthe push buttons of the snap switches so that 2013, 19B and 21B areclosed. It will be readily seen that the closure of contact 19B willeffect energization of the electromagnetic coil 2A which operates in aconventional manner to further out out accelerating resistance in serieswith the armature of the electric motor.

As the cam shaft moves to the high speed position S4 contacts 20A, 19Band 21B are closed, coil 1A being deenergized, so that all of theresistance in series with the armature is cut out and the motor operatesin a conventional manner.

In earlier devices, when the operator desired to reverse the directionin which his electric truck was moving, he would reverse the directionswitch and the controlling elements would then operate so as totend toaccelerate the electric motor in the reverse direction in exactly thesame way as if the truck had been started from rest. The result of thisprocedure was that a serious strain would be placed upon the electricmotor and the drive elements connecting it to the motor truck. In thedevice of the present invention a plugging arrangement is employed whichlimits the torque which may be em ployed to reverse the direction ofmotor rotation to that which is obtainable on the first speed position,so that the extreme stress which was experienced with the use of earlierdevices is thereby eliminated.

This is accomplished in the following manner: with the directioncontrolling switch in, for example, the forward position, when theoperator opens the Forward switch, and closes the Reverse switch, thefirst result is that the electromagnetic coil F is deenergized. Thecontacts controlled by the electromagnetic coil F are thereby returnedto the positions indicated in Figure 10. It will be observed that beforeelectromagnetic coil R can be energized, it is necessary for theoperator to permit the device of the present invention to return to thefirst speed position in which contacts 20A and 19A are closed, as wellas contact 21B. This is done by first releasing the foot pedal so thatits spring effects movement of cam shaft 8 to the off position shown inFigure l. The latching ends of latches 56 drop through the latchingopenings 58 in the rods 6 as the openings 58 are moved upwardly.

The operator then again depresses the foot pedal, so that earn shaft 3moves at a rate determined by the tim ing assembly, from the offposition to the first speed position, in which the coil R is energizedand effects closure of all the normally open contacts marked R, andefiects opening of all the normally closed contacts marked R. Thearmature of the electric motor is connected across the battery throughthe accelerating resistors, and current from the battery will then flowthrough the series field, but in a direction opposite to that originallyused. The armature of the motor, however, is still rotating in theforward direction, and will continue to do so due to inertia, for ashort time. During this time in which the armature continues to rotatein the forward direction while current flows through the series field ina direction which tends to rotate the armature in the reverse direction,the counter-E. M. F. in the armature, instead of opposing the supplyvoltage as is the normal case, will be in the same direction as thesupply voltage. This counter-E. M. F. voltage will be greater than theportion of the supply voltage which is across the armature, due to thefact that the greater portion of the supply voltage appears in thisspeed position across the accelerating r'esistors. Current will,therefore, flow through the coil 45 in a direction opposite to thedirection that current flows through the coil 45 when the counter-E. M.F. opposes the supply voltage. Therefore, the flux emanating from thecoil 45 due to this reverse current flow will tend to attract thepermanent magnet 63 to keep in the position shown in Figure 2, the latchposition 60 of latch 56 thereby holding the rods 6 and preventing themfrom moving under the bias of springs 4. The cam shaft, which is coupledto the rods 6, can therefore not move out of the speed S1 position. Thiscondition will continue until such time as the armature has deceleratedto such a degree that the supply voltage across the armature is highenough to force current to flow through the coil 45 in the normaldirection, which is from left to right in Figure 10. When current flowthrough coil 45 once again is reestablished from the left to the rightin Figure 10; that is to say, in the normal direction, the fluxemanating from this current once again operates against the flux of thepermanent magnet 63 to overcome the sealing effect of the permanentmagnet. The rod 6 can therefore rotate the latch 56 about the pins 55and the cam shaft will move downward toward the high speed position inthe usual manner.

It is obvious that other polarizing methods may be utilized, such asemploying a pair of electromagnetic coils, or by employing a rectifierto control current fiow through coil 45; the particular embodiment shownis, however, more economical.

The device of the present invention will, of course, operate in the samemanner should the truck be moving in the reverse direction when theoperator desires to obtain a forward motion, the coil 45 permittingmovement beyond the first speed position only when the rotation of thearmature has been decreased to a desired speed. The particular point atwhich the holding coil 45 operates to release the latch 56 may beadjusted by moving the connection of the flexible connector 52 todifferent positions along the resistor 53.

As previously indicated, the cam shaft is moved forward at speeds whichare determined by a dashpot timing assembly. The cross section of thisassembly is shown in Figure 7. With the device in the off position, theposition of cam shaft 8 is such that piston 26 abuts against the upperinterior surface of the cylinder 22. In this position, the sealing ring27 which surrounds the plunger 26 is disposed between apertures 31 and32. As may be seen from Figure 7, cylinder 22 is notched adjacentaperture 31 so that piston 26 does not close aperture 31. When cam shaft8 starts to move downwardly under the bias of spring 4 and toward theposition shown in Figure 7, its rate of movement is controlled by therate at which air can pass from the underside of piston 26 throughaperture 32, chamber 29 and aperture 31 into the upper section of thecylinder 22 above the piston 26. This rate of air flow is controlled bythe position of adjusting screw 37. As sealing ring 27 passes aperture32, it also passes aperture 33 which, as previously indicated, lies onthe same transverse plane as aperture 32. The rate of movement of piston26, and therefore the cam shaft 8, is then controlled by the rate atwhich air may pass from aperture 34 through the associated chamber 29and out aperture 33, this rate of air flow being determined by adjustingscrew 33. As rubber ring 27 passes aperture 34, it also passes aperture35 which is coplanar therewith, so that the remainder of the pistontravel is controlled by the rate of air flow between aperture 36 andaperture 35.

The setting of adjusting screws 37, 38 and 39 may or may not be suchthat the piston 26 will move forward, and therefore cam shaft 8 willmove forward, at a uniform rate. If the adjusting screws 37, 38 and 39be set at different positions, the cam shaft 8 will be moved forward bythe springs 4 at varying rates depending upon the particular position ofthe cam shaft in relation to its length of travel. It will therefore beseen that any desired accelerating characteristic may be obtained byadjustment of the adjusting screws 37, 3S and 39. it is, of course,obvious that other accelerating timing controls may be employed if sodesired with the device of the present invention. For example, a dashpot may be employed having but one adjustment feature so that the rateof movement of the cam shaft is uniform over its entire travel. Muchgreater flexibility is, of course, possible through the use of theembodiment shown where each accelerating step is independentlycontrolled in the same device.

It will therefore be seen that the device of the present inventionprovides an extremely useful and yet quite inexpensive means of limitingthe reversing torque which may be applied to any electric motoroperating in one direction to spare the motor and the driving mechanismassociated therewith from the severe shock to which it may otherwise besubject. Furthermore, it will readily be seen that this economicaltorque limiting device is further provided with a timing mechanism whichis adjustable so that any desired acceleration may be accomplished sothat the el ctric motor may be maintained at speed steps a period oftime which is not dependent upon the length at which the electric motoris kept at other speed steps. In addition, these advantageous featuresare obtained with simplicity and economy, the device itself also beingboth rugged and compact.

While certain preferred embodiments or the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestpossible interpretation within the terms of the following claims.

What is claimed is:

l. In a control device, switching means, operating means for saidswitching means movable to eifect switch operation in a predeterminedsequence, an airtight enclosure, a piston operating within saidenclosure and connected to said operating means for controlling themovement thereof, a plurality of individual pairs of interconnectedopenings forming inlet and outlet ports with each individual pairconstituting a separate rate control means f r travel of said pistonbetween the areas of said enclosures as defined by said pairs ofopenings, said openings being longitudinally spaced along and extendingpart way through the wall of said enclosure with the upper opening ofone pair of openings lying in substantially the same longitudinalposition as the lower openings of another of said individual pairs ofopenings, and means for independently varying the rate of fluid flowthrough said individual pairs of interconnected openings whereby therate of movement of said piston is independently variable along thedifferent sections of its travel within said enclosure as defined bysaid individual pairs of openings.

2. in a control device, switching means, operating means for saidswitching means movable to elfect switch operation in a predeterminedsequence, an airtight enclosure, a piston operating within saidenclosure and connected to said operating means for controlling themovement thereof, said enclosure having a plurality of chamhers in itswall and a pair of apertures associated with each of said chambersextending part way through the walls of said enclosure and each one ofsaid pair of apertures communicating the interior or" said enclosurewith the associated chamber, each of said pairs of apertures beingspaced along a diiferent section of the path of movement of said pistonwith one aperture of one of said pairs being substantially coplanar withan aperture of another of said pairs, adjustable means for restrictingthe flow of air through said chambers, said operating means and pistonbeing movable at a rate which depends upon the rate at which air maypass from the portion of said enclosure on one side of said piston tothat portion of said enclosure on the other side of said piston throughsaid, apertures and plurality of chambers, the rate of movement of saidpiston being independently variable. over different sectionsv of itstravel, depending upon the setting of said adjustable means.

3. In a device for controlling the acceleration of an electric motor,switching means, operating means for said switching means movable toeilect switch operation in a predetermined sequence, an airtightenclosure, a piston operating within said enclosure and connected tosaid operating, means for controlling the movement thereof, a pluralityof individual pairs of interconnected openings forming inlet and outletports with each individual pair constituting separate rate control meansfor travel of said piston between the areas of said enclosure as definedby said pairs of openings, said openings being longitudinally spacedalong and extending part way through the wall of said enclosure, a latchfor holding said operating means in a desired position, means formaintaining said latch in latching position, means including anelectromagnetic coil for overcoming the effect of said last mentionedmeans to permit said latch to release said operating means whereby saidoperating means may move to operate said switching means, and means forindependently varying the rate of fluid flow through said individualpairs of interconnected openings whereby the rate of movement of saidpiston is independently variable along difiterent sections of its travelwithin said enclosure as defined by said individual pairs of openings.

4. In a device for controlling the acceleration of an electric motor,switching means, camming means for operating said switching means inpredetermined sequence, biasing means for biasing said camming meanstoward one position, an airtight enclosure, a piston operating withinsaid enclosure and connected to said camming means for controlling themovement thereof, a plurality of individual pairs of interconnectedopenings forming inlet and outlet ports with each individual pairconstituting a separate rate control means for travel of said pistonbetween the areas of said enclosure as defined by said openings, saidopenings being longitudinally spaced along and extending part waythrough the wall of said enclosure, a latch for holding said cammingmeans in a desired position, means for maintaining said latch inlatching positlon, means including an electromagnetic coil forovercoming the elfect of said last mentioned means to permit said latchto release said camming means whereby said camming means may move underthe influence of said biasing means, and means for independently varyingthe fluid flow through said individual pairs of interconnected openingswhereby the rate of movement of said piston and camming means isindependently variable along different sections of travel within saidenclosure as defined by said individual pairs of openings.

5. In a control device, a plurality of switching means, said switchingmeans having rectilinearly movable operators biased toward one position,a plurality of generally U-shaped brackets for effecting operation ofsaid switch operators with the bights of said U-shaped brackets beingcontiguous to said switch operators, an adjusting screw in each of thebights of said U-shaped brackets and aligned with said switch operatorsfor operating said switch operators upon rectilinear movement of saidbrackets, means biasing said brackets toward said switch operators, aroller connected to the open end of each of said U- shaped brackets,camming means extending through the arms of said U-shaped brackets andhaving a plurality of camming surfaces thereon engageable with saidrollers for effecting rectilinear movement of said rollers and brackets,said comming means being rectilinearly movable in a path perpendicularto the planes of movement of said brackets to effect a predeterminedsequence of operation of said switching means.

6. In a control device, switching means, operating means for saidswitching means movable to effect switch operation in a predeterminedsequence, biasing means urging said operating means toward one position,an airtight enclosure, a piston operating within said enclosure andconnected to said operating means for controlling the movement thereof,a plurality of individual pairs of interconnected openings forming inletand outlet ports within each individual pair constituting a separaterate control means for travel of said piston between the areas of saidenclosure as defined by said pairs of openings, said openings beinglongitudinally spaced along and extending part way through the wall ofsaid enclosure, means for independently varying the rate of fluid flowthrough said individual pairs of interconnected openings whereby therate of movement of said piston is independently variable alongdifferent sections of its travel within said enclosure as defined bysaid individual pairs of openings, a latch for holding said operatingmeans in a desired position against the action of said biasing means, apermanent magnet for maintaining said latch in latching position, andmeans including an electromagnetic coil for overcoming the eifect ofsaid permanent magnet to effect the release of said operating means fromsaid latch whereby said operating means may move under the influence ofsaid biasing means to operate said switching means.

7, In a control device, switching means, operating means for saidswitching means movable to effect switch operation in a predeterminedsequence, an airtight enclosure, a piston operating within saidenclosure and connected to said operating means for controlling themovement thereof, said enclosure having a plurality of chambers in itswall and a pair of apertures associated with each of said chambersextending part way through the walls of said enclosure and each one ofsaid pair of apertures communicating the interior of said enclosure withthe associated chamber, each of said pairs of apertures being spacedalong a different section of the path of movement of said piston withone aperture of one of said pairs being substantially coplanar with anaperture of another of said pairs, adjustable means for restricting theflow of air through said chambers, said operating means and piston beingmovable at a rate which depends upon the rate at which air may pass fromthe portion of said enclosure on one side of said piston to that portionof said enclosure on the other side of said piston through saidapertures and plurality of chambers, the rate of movement of said pistonbeing independently variable over diiierent sections of its travel,depending upon the setting or" said adjustable means, means biasing saidoperating means toward one position, a latch for holding said operatingmeans in a desired position against the action of said biasing means, apermanent magnet for maintaining said latch in latching position, anelectromagnetic coil, terminals on said coil for connection to anelectrical circuit, and means mounting said coil adjacent said permanentmagnet whereby said coil overcomes the effect of said magnet uponpredetermined conditions of energization of said coil so that said latchreleases said operating means to effect operation of said switchingmeans.

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